Black Caps coach Mike Hesson says New Zealand cricket must back its core group of players despite being thrashed in two Tests against South Africa.

Speaking the day after South Africa completed a series whitewash with an innings and 193 runs win at St George's Park, Hesson said it was important not to rush into drastic changes.

He identified the failure of the top-order batsmen against South Africa's world-class fast bowling attack as one of the main reasons New Zealand had been outplayed.

"We weren't able to blunt the attack so we were exposing our middle order to the new ball," he said

But he praised the performances of Dean Brownlie and BJ Watling, who had batted well "in extreme conditions".

Hesson said an injury to opening batsman Peter Fulton in a warm-up game had been a big blow. "We were hoping Peter would play a role at the top of the order," he said.

As a consequence, captain Brendon McCullum was forced to open the batting.

"With Ross (Taylor) not there we wanted Brendon at four to give solidity to the middle order. I don't think Brendon's game is suited to blunting an attack."

Although Hesson said McCullum would almost certainly move back to the middle order in the forthcoming series against England, he did not believe in wholesale changes.

"It is about giving players confidence in selection and backing them during a period of time as long as you see improvement," he said.

"We are not going to see instant solutions but if we see people applying themselves and showing the character that is needed at the top of the order, we'll show faith in them. If we keep chopping and changing we'll be going around in circles, which has been an issue for a long time."

Hesson added: "We want to invest time into our core group, although performance needs to be judged."